1. Field of the Invention
The present invention relates to a torque detecting device and an electromotive power steering apparatus mounting the torque detecting device thereon.
2. Description of the Related Art
Of a large number of kinds of torque detecting devices for detecting a torque applied to a rotating shaft, there is typically used a torsion bar spring. As the torque detecting device of this kind, a xe2x80x9csteering torque sensorxe2x80x9d disclosed in JP-A-7-333082 has been known (which will be hereinafter referred to as the xe2x80x9crelated artxe2x80x9d), for example.
According to this related art, as shown in FIG. 20, an input shaft 6 and an output shaft 7 are coupled to each other through a torsion bar spring 8, and a relative torsional angle between the input and output shafts 6 and 7 is detected by detecting coils 2a and 2b. 
The torque detecting device can be mounted on an electromotive power steering apparatus. More specifically, a steering torque applied between the input and output shafts 6 and 7 through a steering wheel is detected by the torque detecting device, and an auxiliary torque corresponding to the steering torque is generated by an electric motor and is applied to a steering system through a reduction gear mechanism, so that the steering torque can be aided with the auxiliary torque. As a result, the steering force of a driver can be relieved to give a comfortable steering sense (steering feeling).
In the related art that the torsion bar spring 8 is used, a relative angle displacement is generated between the input and output shafts 6 and 7 by the torsion of the torsion bar spring 8 corresponding to the torque. In the case in which the torque detecting device is mounted on the electromotive power steering apparatus, a slight time delay is generated on the operation of wheels with respect to the steering operation of the steering wheel.
In particular, in the case in which the auxiliary torque is decreased according to an increase in a vehicle speed to increase the resisting feeling of the steering wheel, the amount of the torsion of the torsion bar spring 8 is increased during the steering when the vehicle speed is increased. The time delay generated according to the amount of the torsion finely influences the steering sense.
On the other hand, in the electromotive power steering apparatus, it is required that the steering sense of the driver should be enhanced as much as possible. In the case in which the conventional torque detecting device is mounted, however, a further enhancement in the steering sense is restricted.
It is an object of the invention to provide (1) a torque detecting device in which the delay of a torque transmission time from the torque input side to the torque output side can be eliminated and the direction and magnitude of an applied torque can be reliably detected with a simple structure and (2) an electromotive power steering apparatus to which such a torque detecting device can be applied.
In order to attain the object, a first aspect of the invention is directed to a torque detecting device wherein a pair of fixed portions are provided on a rotating shaft to have a predetermined distance in an axially longitudinal direction, a permanent strain portion to which a permanent strain is applied by twisting the fixed portions and which changes a magnetostrictive characteristic corresponding to an applied torque is provided between the fixed portions, and a detecting portion for electrically detecting a magnetostrictive effect produced in the permanent strain portion is provided around the permanent strain portion.
The rotating shaft of the torque detecting device is an integral shaft which is not divided into the torque input side and the torque output side. Therefore, when the torque is applied, a very small torsional angle (an angle displacement) is enough. Even if the torsional angle of the rotating shaft is small, it is possible to quickly detect the torque by detecting, through the detecting portion, the magnetostrictive effect produced in the permanent strain portion corresponding to the torque.
Furthermore, there is provided the permanent strain portion for hanging a tool or a jig on a pair of fixed portions and twisting them, thereby applying an accurate permanent strain to the fixed portions in the rotating shaft. In the permanent strain portion, the magnetostrictive characteristic is changed according to the applied torque. By providing the permanent strain portion on the rotating shaft, the origin of the magnetostrictive characteristic curve of the permanent strain portion is shifted from the origin set before the application of the permanent strain. By detecting, through the detecting portion, the magnetostrictive effect produced in the permanent strain portion, it is possible to detect the direction and magnitude of the torque applied to the rotating shaft.
A second aspect of the invention is directed to a torque detecting device wherein a pair of fixed portions are provided on a rotating shaft to have a predetermined distance in an axially longitudinal direction, a magnetostrictive film which is formed of a plated layer to change a magnetostrictive characteristic corresponding to an applied torque and to which a strain is applied by twisting the fixed portions is provided on a surface of the rotating shaft and between the fixed portions with a predetermined width over a whole periphery, and a detecting portion for electrically detecting a magnetostrictive effect produced on the magnetostrictive film is provided around the magnetostrictive film.
The rotating shaft of the torque detecting device is an integral shaft which is not divided into the torque input side and the torque output side. Therefore, when the torque is applied, a very small torsional angle is enough. Even if the torsional angle of the rotating shaft is small, the torque can be detected quickly by detecting, through the detecting portion, the magnetostrictive effect produced in the magnetostrictive film corresponding to the torque.
Furthermore, there is provided the magnetostrictive film for hanging a tool or a jig on a pair of fixed portions and twisting them, thereby applying an accurate strain to the fixed portions in the rotating shaft. In the magnetostrictive film, the magnetostrictive characteristic is changed according to the applied torque. By providing the magnetostrictive film having a strain applied thereto on the rotating shaft, the origin of the magnetostrictive characteristic curve of the magnetostrictive film is shifted from the origin set before the application of the strain. By detecting the magnetostrictive effect produced in the rotating shaft by the detecting portion, it is possible to detect the direction and magnitude of the torque applied to the rotating shaft.
Moreover, it is sufficient that the torque to twist the rotating shaft is so small as to apply a strain to the magnetostrictive film. The torque is such as to loosely twist the rotating shaft in an elastic region. Since it is not necessary to input an excess torque to the fixed portion, the torque can be managed more easily, and furthermore, precision in the torque can be increased. In addition, the torque is such as to loosely twist the rotating shaft in the elastic region. Therefore, equipment for inputting a torque to the fixed portion can have a simple and light structure.
A third aspect of the invention is directed to an electromotive power steering apparatus mounting the torque detecting device according to the first or second aspect of the invention as a steering torque sensor for detecting a steering torque of a steering system which is generated on a wheel for a vehicle.
In the third aspect of the invention, the rotating shaft is a pinion shaft to be rotated through a universal joint by means of the steering wheel, one of the fixed portions is a spline coupling portion or a serration coupling portion which is formed on one of ends of the pinion shaft which is to be coupled to the universal joint, and the other fixed portion is a pinion of a rack and pinion mechanism to be coupled to a steering wheel.
The rotating shaft of the torque detecting device mounted on the electromotive power steering apparatus is an integral shaft which is not divided into the torque input side and the torque output side. Therefore, when a steering torque is applied, a very small torsional angle is enough. For this reason, a time delay is not caused on the operation of the wheel as compared with the steering of a steering wheel. Accordingly, it is possible to further increase the responsiveness of the electromotive power steering apparatus which generates an auxiliary torque corresponding to the steering torque and aids. Consequently, a steering sense can be enhanced still more.
In particular, also in the case in which the resisting feeling of the steering wheel is increased by decreasing the auxiliary torque corresponding to an increase in a vehicle speed, the torsional angle of the rotating shaft may be very small. Consequently, when steering the steering wheel, a steering angle thereof can be directly transmitted to the wheel so that comfortable steering having a high responsiveness can be carried out.
Furthermore, the spline coupling portion or the serration coupling portion in the rotating shaft is also used for one of the fixed portions and the pinion of the rotating shaft is also used for the other fixed portion. Therefore, it is not necessary to provide the fixed portion to be twisted by hanging a tool or a jig thereon. Accordingly, the rigidity of the rotating shaft can be further increased.
A fourth aspect of the invention is directed to a torque detecting device wherein a first fixed portion, a second fixed portion and a third fixed portion are sequentially provided on a rotating shaft to have a predetermined distance in an axially longitudinal direction, a first permanent strain portion to which a permanent strain is applied by twisting the first and second fixed portions and which changes a magnetostrictive characteristic corresponding to an applied torque is provided between the first and second fixed portions, a second permanent strain portion to which a permanent strain different from that of the first permanent strain portion is applied by twisting the second and third fixed portions and which changes a magnetostrictive characteristic corresponding to an applied torque is provided between the second and third fixed portions, and a detecting portion for electrically detecting a magnetostrictive effect produced in the first and second permanent strain portions is provided around the first and second permanent strain portions.
The rotating shaft of the torque detecting device is an integral shaft which is not divided into the torque input side and the torque output side. Therefore, when the torque is applied, a very small torsional angle is enough. Even if the torsional angle of the rotating shaft is small, the torque can be detected quickly by detecting, through the detecting portion, the magnetostrictive effect produced in the permanent strain portion corresponding to the torque.
Furthermore, the first and second permanent strain portions to which accurate permanent strains different from each other are applied are provided between the first, second and third fixed portions in the rotating shaft by twisting the tools or jigs hung on the first, second and third fixed portions. In the first and second permanent strain portions, the magnetostrictive characteristics are changed corresponding to the applied torque. By providing the first and second permanent strain portions on the rotating shaft, the origins of the magnetostrictive characteristic curves of the first and second permanent strain portions are shifted from the origin set before the application of the permanent strain.
The magnetostrictive characteristic of the second permanent strain portion is different from that of the first permanent strain portion. It is possible to detect the direction and magnitude of the torque applied to the rotating shaft by detecting, through the detecting portion, each of the magnetostrictive effects produced in the first and second permanent strain portions having the magnetostrictive characteristics different from each other, and furthermore, to carry out the failure diagnosis of the torque detecting device by comparing two different detection values.
In addition, if a difference between the two different detection values is varied within a torque measurement range, it is possible to eliminate the influence of a temperature characteristic, thereby obtaining a stable signal characteristic based on the difference between the two detection values. Thus, it is possible to obtain a more excellent torque detection signal which is not varied according to a change in an environmental temperature.
A fifth aspect of the invention is directed to a torque detecting device wherein a first fixed portion, a second fixed portion and a third fixed portion are sequentially provided on a rotating shaft to have a predetermined distance in an axially longitudinal direction, a first magnetostrictive film which is formed of a plated layer to change a magnetostrictive characteristic corresponding to an applied torque and to which a strain is applied by twisting the first and second fixed portions is provided on a surface of the rotating shaft and between the first and second fixed portions with a predetermined width over a whole periphery, a second magnetostrictive film which is formed of a plated layer to change a magnetostrictive characteristic corresponding to an applied torque and to which a different strain from that of the first magnetostrictive film is applied by twisting the second and third fixed portions is provided on the surface of the rotating shaft and between the second and third fixed portions with a predetermined width over a whole periphery, and a detecting portion for electrically detecting a magnetostrictive effect produced in the first and second magnetostrictive films is provided around the first and second magnetostrictive films.
The rotating shaft of the torque detecting device is an integral shaft which is not divided into the torque input side and the torque output side. Therefore, when the torque is applied, a very small torsional angle is enough. Even if the torsional angle of the rotating shaft is small, the torque can be detected quickly by detecting, through the detecting portion, the magnetostrictive effect produced in the first and second magnetostrictive films corresponding to the torque.
Furthermore, the first and second magnetostrictive films to which accurate strains different from each other are applied are provided between the first, second and third fixed portions in the rotating shaft by twisting tools or jigs hung on the first, second and third fixed portions. In the first and second magnetostrictive films, the magnetostrictive characteristics are changed corresponding to the applied torque. By providing the first and second magnetostrictive films on the rotating shaft, the origins of the magnetostrictive characteristic curves of the first and second magnetostrictive films are shifted from the origin set before the application of the strain.
The magnetostrictive characteristic of the second magnetostrictive film is different from that of the first magnetostrictive film. It is possible to detect the direction and magnitude of the torque applied to the rotating shaft by detecting, through the detecting portion, each of the magnetostrictive effects produced in the first and second magnetostrictive films having the magnetostrictive characteristics different from each other, and furthermore, to carry out the failure diagnosis of the torque detecting device by comparing two different detection values.
In addition, if a difference between the two different detection values is varied within a torque measurement range, it is possible to eliminate the influence of a temperature characteristic, thereby obtaining a stable signal characteristic based on the difference between the two detection values. Thus, it is possible to obtain a more excellent torque detection signal which is not varied according to a change in an environmental temperature.
Moreover, it is sufficient that the torque to twist the rotating shaft is so small as to apply a strain to the first and second magnetostrictive films. The torque is such as to loosely twist the rotating shaft in an elastic region. Since it is not necessary to input an excess torque to the first, second and third fixed portions, the torque can be managed more easily, and furthermore, precision in the torque can be increased. In addition, the torque is such as to loosely twist the rotating shaft in the elastic region. Therefore, equipment for inputting a torque to the first, second and third fixed portions can have a simple and light structure.
A sixth aspect of the invention is directed to an electromotive power steering apparatus mounting the torque detecting device according to the fourth or fifth aspect of the invention as a steering torque sensor for detecting a steering torque of a steering system which is generated on a wheel for a vehicle.
In the sixth aspect of the invention, the rotating shaft is a pinion shaft to be rotated through a universal joint by means of the steering wheel, the first fixed portion is a spline coupling portion or a serration coupling portion which is formed on one of ends of the pinion shaft which is to be coupled to the universal joint, and the third fixed portion is a pinion of a rack and pinion mechanism to be coupled to a steering wheel.
The rotating shaft of the torque detecting device mounted on the electromotive power steering apparatus is an integral shaft which is not divided into the torque input side and the torque output side. Therefore, when a steering torque is applied, a very small torsional angle is enough. For this reason, a time delay is not caused on the operation of the wheel as compared with the steering of a steering wheel. Accordingly, it is possible to further increase the responsiveness of the electromotive power steering apparatus which generates an auxiliary torque corresponding to the steering torque and aids. Consequently, a steering sense can be enhanced still more.
In particular, also in the case in which the resisting feeling of the steering wheel is increased by decreasing the auxiliary torque corresponding to an increase in a vehicle speed, the torsional angle of the rotating shaft may be very small. Consequently, when steering the steering wheel, a steering angle thereof can be directly transmitted to the wheel so that comfortable steering having a high responsiveness can be carried out.
Furthermore, the spline coupling portion or the serration coupling portion in the rotating shaft is also used for the first fixed portion and the pinion of the rotating shaft is also used for the third fixed portion. Therefore, the second fixed portion is enough for the fixed portion to be twisted by hanging a tool or a jig thereon. Accordingly, the rigidity of the rotating shaft can be further increased.